1. Field of the Invention
The invention is related to the field of switch migration, and in particular, to a tandem switch migration method.
2. Statement of the Problem
On occasion, the routing of communications between end users and an associated telephone network must necessarily be modified. For example, one or more switches may need to be replaced, upgraded, etc. If a node (such as a local switch) and an associated tandem switch are to be replaced, then many end users (and possibly multiple nodes) may need to be migrated to a new tandem switch. When a switch is to be replaced, the outbound and inbound calls must be changed over to the new tandem switch in order to ensure that all calls are delivered. It is imperative that the migration be accomplished swiftly in order to avoid or minimize a drop in service availability. The migration should be executed in a manner that enables the old node or nodes to be quickly and easily re-deployed if a problem occurs during the migration. If the migration is not successfully completed, the result can be a loss of service. In a worst case, the result can be an unacceptably long loss of service. If the migration is not properly and efficiently designed, the result can be a difficult, costly, and time-consuming change back to the original configuration and necessity to re-conduct the migration at a later time.
Local number portability is a scheme for allowing persons (and/or institutions) to keep an existing telephone number when moving to a new location or when switching to a new service provider. The LNP process is transparent to the caller and to the called party.
Before local number portability, telephone numbers were assigned to a local service-provider's end offices on an NPA-NXX basis. An NPA-NXX is defined as the Numbering Plan Area (NPA) and an office code (NXX) of an end user's telephone number (e.g., 123-456-7890). Each NPA-NXX can include up to 10,000 different telephone numbers. In the past, a telephone number identified the person/telephone, as well as the actual end office or telephone switching system that served the person. As a result, the dialed NPA-NXX was the terminating switch's routing address to the rest of the network. With the implementation of LNP, which allows any number of local service providers to serve the same NPA-NXX, this routing scheme could no longer be used.
The LNP architecture utilizes a unique 6-digit LRN to identify each switch in the network for call routing purposes. Each switch is assigned a LRN. Consequently, a LNP information entry correlates a dialed (i.e., destination) telephone number to a LRN of a terminating switch. The LRN is used to route the call to the terminating switch, and the original dialed telephone number is then used by the terminating switch to complete the call.
A LNP information (such as a LNP database, for example) is used to store the routing information for subscribers who have moved or ported to another local service provider. The LNP database can be accessed by a switch in order to route a call to a ported telephone number.
FIG. 1 shows a conventional, prior art LNP process, wherein a destination telephone number has been ported using the LNP capability. The source telephone initiates a telephone call to the destination telephone by dialing a destination telephone number. The dialed number is received in a local (originating) switch. The originating switch can signal a routing resource, such as a Signal Control Point (SCP), in order to obtain routing information for the destination telephone. The originating switch performs a “LNP dip” and accesses a LNP database or other LNP information. If the dialed number is in the LNP database, the telephone number has been ported via local number portability. If the dialed number is not in the LNP database, the dialed number is used to route and connect the telephone call. In this example, the LNP dip produces a 10 digit number, wherein the LRN is the first 6 digits. Herein the term subLRN refers to the use of all 10 digits for routing and connecting the telephone call, rather than using just the 6 digit LRN. This 10-digit number is substituted into a Called Party Number field (CdPN) of the call signaling, replacing the dialed number. The dialed number, however, is retained in a Generic Address Parameter (GAP) field of the call signaling for future use. The SCP provides the LRN and the dialed number back to the originating switch. The originating switch then routes and connects the telephone call to the terminating switch. The telephone call can transit any number of intermediate switches. The terminating switch receives the telephone call, according to the LRN (i.e., the first 6-digits of the CdPN). The terminating switch recognizes it's LRN, retrieves the dialed number from the GAP, and connects the telephone call to the destination telephone.